Powder coatings compositions for use in coating various types of substrates are often desired. Such coating compositions can greatly reduce, or even eliminate, the use of organic solvents that are often used in liquid coating compositions. When a powder coating composition is cured by heating, little if any volatile material is given off to the surrounding environment. This is a significant advantage over liquid coating compositions in which organic solvent is volatized into the surrounding atmosphere when the coating compositions is cured by heating.
In many applications, such as many outdoor applications, powder coating compositions that produce coatings having reduced gloss are desired. Low gloss coatings can be achieved by creating a surface that is rough on a microscopic scale, thus scattering incident light on the micro-structured surface, while retaining a smooth macroscopic appearance.
In liquid coating compositions, gloss reduction is often achieved by the use of pigment and/or filler particles in high volumes. While this approach is sometimes used in powder coating compositions, a large amount of fillers are often required to achieve a desired gloss level in powder coating applications due to the absence of film shrinkage during cure. As the amount of such fillers in powder coating compositions increases, a significant loss in mechanical properties of the cured coating often occurs. The difficulty in achieving low gloss coatings from powder coating compositions is exacerbated when low temperature cure (<300° F.) is required.
In some cases, low gloss coatings have been produced from powder coating compositions comprising incompatible components, such as film-forming resins that are incompatible with each other. One difficulty that has been experienced with this mechanism, however, is that it has been difficult, if not impossible, to achieve consistent stable gloss values from such coatings. Differences in oven temperature and reaction rates between the incompatible components can render the variation in gloss of the resultant coating difficult, if not impossible, to control. As a result, it has been difficult to produce stable mid-gloss range coatings from powder coating compositions.
Thus, it would be desirable to provide powder coating compositions that are capable of producing mid-gloss coatings. It would also be desirable to provide methods for producing mid-gloss coatings from powder coating compositions.